The walls of arteries and blood vessels can become damaged by disease or a number of other causes, including medical treatments such as angioplasty. One technique that has been used to repair damaged vessels and arteries is invasive surgery. Typically, incisions are made in the area of the damaged vessel, and it is resected and replaced either by a synthetic graft or by a healthy vessel that is removed from the patient at a different portion of his or her body. The graft is typically sutured in place. While this technique is often effective, it is characterized by the trauma and other problems that are associated with major surgery. In the case of patients who are in poor health or in a weakened condition, invasive surgery is not always possible.
As disclosed in U.S. Pat. No. 5,078,726 to Kreamer, prior inventors have proposed holding vascular grafts in place through the use of expansible stents. The principal problems with the stents proposed in the Kreamer patent is that they are naturally contracted and must be positively expanded in order to be able to hold the graft in place. Consequently, a balloon catheter or other device must be inserted into the vessel to the area of the stents and expanded in order to expand the stents. The need to make use of a balloon catheter increases the difficulty involved in properly applying the graft. In addition, it increases the time that is needed for the procedure and requires highly skilled and experienced medical personnel. The stents are not always properly applied even then, and their ability to hold the graft in place suffers accordingly.
Another drawback with the Kreamer device is that the stents have a fixed diameter in the expanded condition. Consequently, it is necessary for the stent to closely conform with the diameter of the blood vessel in order to properly perform its intended function. If the stent is too large, it can unduly expand and the healthy part of the vessel against which it presses. Conversely, a stent that is too small is unable to securely hold the graft in place. Thus, in order for the system proposed by Kreamer to function properly, the stents must be provided in a wide variety of sizes, and the proper size must be selected for each different application. Again, this increases the costs and complexity involved in the overall procedure and adds to the risk of improper graft placement.